1. Field of the Invention
The invention relates to a fuel injection system, and particularly to a fuel injection system for internal combustion engines including a metering valve in the fuel injection pressure line.
2. Description of the Prior Art
For the sake of better understanding of the specification and claims, several terms will first be explained: The fuel injection system according to the invention is embodied as pressure-controlled. Within the scope of the invention, the term pressure-controlled fuel injection system is understood to mean that by the fuel pressure prevailing in the nozzle chamber of an injector, a valve member is moved counter to the action of a closing force (spring), so that the injection opening is uncovered for an injection of the fuel from the nozzle chamber into the cylinder. The pressure at which fuel emerges from the nozzle chamber into a cylinder of an internal combustion engine is called the injection pressure while the term system pressure is understood to mean the pressure at which the fuel is available or kept in reserve within the fuel injection system. Fuel metering means furnishes a defined fuel quantity for injection. The term leakage is understood to mean a quantity of fuel which occurs in operation of the fuel injection system (such as guide leakage), which is not used for injection, and which is pumped back to the fuel tank. The pressure level of this leakage can have a static pressure, in which case the fuel is pressure-relieved to the pressure level of the fuel tank.
In common rail systems, the injection pressure can be adapted to the load and rpm. For noise abatement, a preinjection is often performed in this case. Pressure-controlled injection is known to be favorable for reducing emissions. In the known pressure-controlled common rail systems, however, either one 3/2-way valve, which is complicated to manufacture, or two 2/2-way valves are used per injector.
To lower the cost of producing the fuel system, especially for small engines, a fuel injection system is proposed. Using a single 2/2-way valve, as the metering valve, per cylinder leads to a more-economical system. After the termination of injection, relief of the nozzle chamber by means of a pressure relief valve or a pressure relief throttle, which are disposed in the communication of the pressure storage chamber with the injector, is necessary to avoid a postinjection. The use of a permanently open and additionally actuatable pressure relief throttle makes it easier to design the system without xe2x80x9cafter-injectionsxe2x80x9d. An additional hydraulic closing force on the valve member speeds up the closing operation and also prevents unwanted opening of the valve member from pressure fluctuations in the system. If instead of a seat-type or blind bore nozzle the injector has a vario-nozzle or vario-register nozzle, then the course of injection can be adapted even better to the requirements of the engine.